Anyone remember these now obsolete units? I bought one 10 or 12 yrs ago to use with my SX-28. Despite my lack of training and expertise I managed to complete the assembly and adjust it for use with the intended receiver. It worked very nicely. Then one day, never having acquired a frequency counter, I "undid" the LO offset to use it as a frequency counter

Now I would like to return the DFD1 to its intended use. But I can't remember how it's coupled to the receiver (I can find only a few pages of the original documentation, and not the one for those instructions). Through a small cap to the grid or cathode pin of the mixer tube? Or the oscillator tube? Both are 6SA7s. I tried that and the display is not reacting to whatever signal is present on either pin 5 or pin 6 of either tube.

To test that it actually works, I coupled it to the oscillator of another radio. It worked, although the display showed twice the nominal frequency of the oscillator. So, any suggestions for the SX-28? Thanks!

I have one of those and in order to get mine to work with my SP-600 without pulling the oscillator frequency while getting a reliable display I had to use the preamp board (mounted it inside the case) and mount a jack on the radio chassis near where a wire carrying the LO signal runs.